Klystrons



R. DUNSMUIR Jan. 27, 1959 KLYSTRONS Filed Aug. 20, 1957 ROBERT oqu m I HT TO RNE Y IN VEN TOR United at at nt KLYSTRONS Robert Dunsmuir, Rugby, England, assignor to The British Thomson-Houston Company Limited, London, England, a British company Application August 20, 1957, Serial No. 679,239

Claims priority, application Great Britain August 21, 1956 1 Claim. (Cl. 315-539) This invention relates to velocity modulated electron discharge devices and more particularly to klystrons.

The method of operation of a klystron is well known. An electron beam is projected through two or more cavities in series. The R. F. signal which it is desired to amplify is injected into the first cavity, i. e. the buncher, which is arranged to be resonant at or near the frequency of the signal. This causes the electrons passing through the cavity to be bunched in a related manner. The second cavity or catcher resonator is also tuned to be resonant near to the operating frequency, and the bunched electrons in passing through it, produce across the gap an R. F. voltage. For the maximum efiiciency the R. F. voltage effective on the electrons should be nearly equal to the beam voltage.

To operate satisfactorily over a wide bandwidth, the second cavity must have a low Q, and thus a low value of shunt resistance R, since Q=RwC, where w is the I angular frequency and C is the gap capacity.

However, power output where Vrf is the peak R. F. voltage across the gap, and since R is required to be low, for a given power output Vrf is also low, and may be much less than the electron gun voltage V,. Thus a valve with a broad band width characteristic has a low efliciency.

The efiiciency would be increased if several catcher" resonators were arranged in series, and their outputs were combined. It is evident, however, that in such an arrangement the common output circuit would provide a ready feed-back path between the catcher resonators, with the result that the system would oscillate.

The object of the present invention is to provide a klystron having several catcher resonators, and therefore having a higher efficiency, but which nevertheless does not tend to oscillate.

The present invention comprises a klystron having a buncher resonator and a plurality of catcher" resonators distributed along the electron beam, each of which catcher resonators is coupled to a common output circuit through a separate ferrite isolator.

The term ferrite isolator implies a device which, operating on the Faraday Rotation principle, transmits in one direction only. Such arrangements are described in Electronic Engineering, August 1956, at page 328.

It is well known that two rectangular waveguides can be coupled together by means of a ferrite device, in such a way that electromagnetic energy within a particular frequency band can be transmitted from the first waveguide into the second waveguide,.but not from the second waveguide into the first waveguide. If, therefore, each catcher resonator is connected to the common output 2,871,396 Patented Jan. 27, 1959 ice 2 circuitthrough such a ferrite isolator. it=can ;bfl arranged that energy is fed into the output circuit from .each

catcher resonator, but no energy can be transmitted from one catcher resonator to another via the output circuit. Thus feedback is prevented and therefore no oscillatory tendency is present.

In order that the invention may be more fully understood reference will now-be made to the accompanying drawing which shows in diagrammatic form one embodiment of the invention.

In the drawing the reference 1 indicates a klystron drift tube having a buncher. resonator 2 positioned at the in put end thereof and catcher resonators 3, 4 and 5 distributed in sequence along the line of the electron beam near the output end of the tube. An electron gun 6 is maintained at a large potential which is negative with respect to drift tube 1 so as to cause electrons to be injected at high velocity into tube 1. These electrons are bunched by buncher resonator 2 and progress along the drift tube 1 to electron collector 7.

' Each individual catcher resonator 3, 4 and 5 is coupled to a'common output circuit 14 through individual feeder means 21, 22 and 27. The feeder means respectively include coupling irises 8, 9 and 10 between the resonators 3, 4 and 5 and output windows 11, 12 and 13 which hermetically seal the klystron from its output circuit and enable it to be maintained as a vacuum enclosure.

Feeder means 22 and 27 include phase changers 15 and 16 as shown to enable the phase of the outputs from these feeder means to be adjusted to ensure that additive combination occurs in output circuit 14. The feeders also include ferrite isolators 17 and 18 which allow electromagnetic energy to be transmitted in one direction only as indicated by the arrows.

Feeders '21 and 22 are coupled together by means of a 3 db directive coupler 23, the output arm 25 of which leads directly into output circuit 14 while a matched load 24 is provided in the fourth arm thereof to prevent reflections. A further 3 db coupler'26 couples together the outputs from feeder 27 and arm 25 in cascade directly into output circuit 14. To prevent undesirable reflections a matched load 28 is provided in the fourth arm of coupler 26. Alternatively, other forms of directive couplers, such as magic T couplers may be used.

By providing coupling flanges 30, 31 and 32 in the feeder arms from the catcher resonators, the klystron itself may be constructed as a separate unit from its output circuit.

In operation the phases of the outputs of the feeder means are adjusted by phase changers 15 and 16 to ensure that the output waves additively combine in output circuit 14 rather than interfere destructively or be dissipated in the isolators. These adjustments may be preset by providing suitable lengths of waveguide or else may be controllable by means of phase changers as shown in the figure.

Clearly although in the described embodiment three catcher resonators are shown the invention is not limited thereto but a greater or less number of catchers may be employed. It will be realised, however, that the ferrite isolators and phase changes are only needed in all but one of the feeder means.

What I claim is:

A klystron comprising an electron gun for developing an electron beam and including a buncher resonator, a plurality of catcher resonators which are distributed in sequence along the line of the electron beam, individual feeder paths from each of said catcher resonators, phase changers positioned in at least some of said feeder paths,

couplers each having 'two inputs one of which is com-' men and a single output into which output the energy from the two inputs is combined, said feeder paths being coupled to the inputs of some directive couplers the outputs of which are coupled to the inputs of further directive couplers in cascade so that all the feeder paths combine into a final common output.

References in the file of this patent UNITED STATES' PATENTS Pierce June 12, 1951 Garbuny July 29, 1952 Luhrs et al.'. July 7, 1953 Sensiper Sept. 17, 1957 Chodorow Nov. 19, 1957 

